Resins such as polyamides and polyacetals, because of their low friction coefficient and excellent mechanical strength and chemical stability, are widely used in the fabrication of molded articles that require lubrication, such as bearing bushings, gears, cams, rollers, bearings, switch sliders and fasteners.
However, even these resins are not always able to deliver a satisfactory performance under relatively demanding conditions such as those encountered in rolling stock and industrial machinery. Hence, lubrication with substances such as oil or grease is normally carried out. However, in lubrication with oil or grease, loss of lubrication may occur over time as the oil or grease comes off the sliding or mating surface during use. Deleterious effects that arise with loss of lubrication include increased energy required to overcome the resulting increased friction at moving surfaces and rapid wear of the molded article.
One approach to this problem that has been taken in the prior art involves impregnating a lubricating oil into the resin (such as polyacetal, polyamide or polyphenylene sulfide) making up the molded article requiring lubrication, and using the impregnated lubricating oil to carry out lubrication (see JP-B 46-42217, JP-B 46-5231, JP-B 47-42615 and JP-B 48-7865). JP 2003-286196 A discloses porous particles impregnated with substances such as pigments, perfumes, agrochemicals, or medicines. JP 2002-346381 A discloses water-absorbing fine particle material.
However, when a resin impregnated with lubricating oil is subjected to heat and pressure during molding, the lubricating oil separates out, making it impossible to carry out molding using conventional pellets. Moreover, when components that have been manufactured from a lubricating oil-impregnated resin are used over an extended period of time, the coefficient of friction between the components and the surfaces against which they are in motion increases, thus increasing the amount of wear. Accordingly, there has existed a need for resin compositions capable of maintaining a low coefficient of friction coefficient and low levels of wear over an extended period of time.
There has also been a strong desire for resin compositions that do not experience loss of lubrication and are able to maintain a low coefficient of friction and minimize wear over time.
It is desirable for the present invention to provide resin compositions, which contain a thermoplastic resin and a lubricant-impregnated mesoporous powder. It is also desirable that the present invention provides articles shaped from such compositions.